The present invention relates to temperature control apparatus wherein a cooling vent is operated incrementally and heat is otherwise supplied to facilitate temperature regulation near room ambient conditions. Such apparatus is commonly known but in the prior art apparatus, the cooling vent is only operated to be closed or fully opened and therefore, temperature regulation becomes difficult near room ambient set points because fluctuations commonly occur about the set point when increased heat loss is required to maintain control and considerable thermal gradients occur within the thermal system. Consequently, control response is slow and heat is supplied while the thermal system is below the temperature set point during each cycle of fluctuation, which are both undesirable for many obvious reasons to those skilled in the art of thermal systems.